Fall through on missing $ViewInjector

I think I did this correctly. The goal is to allow `Views.inject(this)` (for example, `this isinstanceof Activity`) to be valid independent on a `ViewInjector` being constructed for it. As in, you can define this to be performed in your `Activity`s' `onCreate`, and even if you don't `@InjectView`s in it.

What do you think of that idea?